Annular magnet core built up from a soft magnetic ferrite material and method of manufacturing the same

ABSTRACT

ANNULAR FERRITE CORES HAVING AN OUTSIDE DIAMETER NOT EXCEEDING 0.6 MM. AND AN INSIDE DIAMETER OF AT LEAST HALF OF THE OUTSIDE DIAMETER AS MEMORY CORES IN ELECTRONIC COMPUTERS HAVING A COMPOSITION EXPRESSED IN MOLAR PERCENTAGES OF THE FERRITE-FORMING OXIDES WITHIN THE FOLLOWING RANGE: 74.5-80.0 MOLE PERCENTAGE FE2O3; 12.5-14.6 MOLPERCENT LI2O; 3.0-8.0 MOL PERCENT ZNO; AND MAXIMALLY 6.1 MOL PERCENT NIO. THESE CORES HAVE PLUSE CHARACTERISTICS WHICH ARE SUBSTANTIALLY TEMPERATURE-INSENSITIVE OVER AN EXTREME TEMPERATURE RANGE, AND ARE RESPONSIVE TO COMPARTIVELY WEAK CURRENT PULSES. IN THE MANUFACTURE OF THESE MAGNET CORES THEY ARE COOLED, AFTER HEATINGS, TO ROOM TEMPERATURE AT A SUBSTANTIALLY CONSTANT SPEED.

United States Patent Office 3,717,578 Patented Feb. 20, 1973 ANNULARMAGNET CORE BUILT UP FROM A SOFT MAGNETIC FERRITE MATERIAL AND METHOD OFMANUFACTURING THE SAME Nicolaas Petrus Slijkerman and Cornelis JacobusEsveldt, Emmasingel, Eindhoven, Netherlands, assiguors to US. PhilipsCorporation, New York, N.Y.

No Drawing. Continuation of abandoned application Ser. No. 831,762, June9, 1969. This application May 27,

1971, Ser. No. 147,656 Claims priority, application 1Nleztherlands, June8, 1968, Int. Cl. C04b 35/26 US. Cl. 252-62451 3 Claims ABSTRACT OF THEDISCLOSURE cooled, after heating, to room temperature at a substantiallyconstant speed.

This application is a continuation of application Ser. No. 831,762,filed June 9, 1969, now abandoned.

It is known to use annular magnet cores built up from a soft magneticferrite material as memory elements in electronic computers. For thesememory elements a large speed, that is to say a very short switchingtime, is one of the principal requirements for use. The switching time(2,) is to be understood to mean the time which elapses between theinstant at which the current intensity of the reading pulse (testcurrent) has risen to an amount of of its maximum value and the instantat which the voltage pulse induced in the reading wire has fallen to anamount of 10% of its maximum value. The smaller the dimensions of thememory element, at a much lower control current a suflicient low valueof the switching time is reached, that is to say, the element is moreeconomical to use.

For various applications of memory elements it is also important thattheir pulse characteristics show substantially constant values over alarge temperature range.

The memory elements according to the invention which have an outsidediameter of not exceeding 0.6 mm., and an inside diameter of at leasthalf of the outside diameter are distinguished in that at a testcurrent, I not exceeding 750 ma.:

(a) t the switching time, is smaller than 0.25 ,usec.- (b) 1N i.e. themaximum value of the output voltage upon reading of an undisturbed onesignal which is caused by the first reading pulse, is at least 40 mv.;(c) the quotient (where aV is the maximum value of the output voltage ofa zero signal interfered frequently with an interfering writing pulse)at an interference ratio of 0.61

has a value of at least 3.5; interference ratio is to be understood tomean the value of the quotient of an interference-test pulse, I and afull test pulse, I (d) in the temperature range between 0 C. and 60 C.

a control current compensation not exceeding 1.9 ma./

C. is suflicient. Control current compensation is to be understood tomean the decrease of the test current (in ma.) necessary to maintain theoutput voltage at the same value at an increase of the temperature byThe range of compositions of the magnet cores according to the inventionis characterized by the following percentages of the metal oxidesinvolved in forming the ferrite material, namely iron oxide, lithiumoxide, zinc oxide and, if desirable, nickel oxide: 74.5-80.0 mol.percent Fe O 12.5-14.6 mol. percent Li O; 3.0-8.0 mol. percent ZnO; andup to 6.1 mol. percent NiO.

The preparation of the magnet cores according to the invention ispreferably carried out as follows. The new materials, usually theabove-mentioned metal oxides which, however, may individually bereplaced partly or entirely by other compounds of the relative metalswhich upon heating are converted into the corresponding metal oxides,are ground in a ball mill for approximately 4 hours and at the same timemixed. The dried mixture is prefired in a fluidized bed furnace afterwhich the prefired product is cooled and ground to a very fine powder inthe course of approximately 16 hours. This powder is the suspended inacetone, while adding a binder, after which the suspension is atomizedin a heated space. The resulting granules are compressed to rings of thedesired dimensions which rings are sintered after removing the binder byheating at approximately 300 C. The prefired powder may alternatively bemixed with a binder to form a paste and this paste may be evenly smearedon a supporting foil consisting of a suitable synthetic resin in a layerof the desirable thickness and may then be left to dry thereon, afterwhich the ferrite layer is detached from the supporting foil and ringsof the desired dimensions are punched from it, which rings are sinteredagain after removing the binder by heating at approximately 300 C.

The sintering of the rings is preferably carried out as follows: Anumber of rings are provided in a platinum boat and this is arrangedwithin one minute, preferably in approximately 30 seconds, in thehottest region of a furnace where a temperature between 1100 C. and 1200C. prevails. The boat with the rings is kept in said region for 1 /2 to8 minutes and is then pulled out of the furnace gradually at asubstantially constant speed so that the rings are cooled to roomtemperature in a period of time varying from 5 to 25 minutes preferablywithin 8 to 20 minutes. The principal pulse characteristics are thenmeasured in the resulting rings. The interference ratio used in themeasurements is always 0.61.

In order that the invention may be readily carried into effect, a fewexamples thereof will now be described in greater detail.

For sintering the rings (which have an outside diameter of approximately0.5 mm. and an inside diameter of approximately 0.3 mm.) the ringswere'arranged in a platinum boat in the hottest region of a furnace in aperiod of time of approximately 30 seconds in which region a temperatureprevailed of 1105 C. Two minutes later the boat with the rings waspulled out of the furnace at a substantially constant speed. Twentyminutes afterwards the rings were cooled to room temperature.

The results of the measurements performed in the resulting magnet coresare stated in the stable after Example V. In addition to the measuredvalues of the above-defined quantities the measured values of thequantities rV and t rV which is to be understood to means the maximumvalue of the output voltage upon reading a one signal frequentlyinterfered with an interfering-reading pulse which is caused by thesecond reading pulse also recorded in the table. The peak time, t is tobe understood to means the period between the instant at which thecurrent intensity of a full reading pulse has increased to an amount ofof its maximum value and the instant at which the output voltage causedby said pulse reaches its maximum value.

EXAMPLE II The composition of the starting mixture was as follows:

Mol percent Fe O 79.04 Li O 14.51 ZnO 5.00 NiO 1.45

The rings (which have an outside diameter of approximately 0.5 mm. andan inside diameter of approximately 0.3 mm.) were sintered mainlyaccording to the prescription of Example I, with the difference that thetemperature in the hottest region of the furnace now was 1169 C. Thesintering time was again 2 minutes. Then the boat with the rings waspulled out of the furnace at a substantially constant speed in suchmanner that the rings were EXAMPLE IV The composition of the startingmixture was as follows:

Mol percent FEZOK Li O u 13.61 ZnO 3.13

The rings had an outside diameter of approximately 0.4 mm. and insidediameter of approximately 0.25 mm. The rate of heating was againapproximately 30 seconds. In the hottest furnace region temperature of1165 C. prevailed. The rings were kept in said region for 2 minutes.Then the boat with the rings was pulled out of the furnace at asubstantially constant speed, so that in a period of time ofapproximately 8 minutes they were cooled to room temperature.

The measured results of the resulting rings are again recorded in thetable after Example V.

EXAMPLE V The composition of the starting mixture was as follows:

" Mol percent F8203 76.12 N1 0 13.06 ZnO 5.01

NiO 5.81

TABLE Current; compensation Magnet cores I uV 7V dVz t, 11,, 11V between0 C. according to (milli- (ruilli- (milli- (milli- (micro- (microand 600. example number amperes) volts) volts) volts) seconds) seconds) dVz(11111 per C.)

cooled to room temperature after another 11 minutes.

The measured results obtained in the resulting rings are again recordedin the table after Example V.

EXAMPLE III The composition of the starting mixture was as follows:

Mol percent Fe O 77.21 Li O 13.61 ZnO 3.13

NiO 6.05

' stant speed in such manner that the rings were cooled to roomtemperature after approximately another 9 minutes. The measured resultsof the resulting rings are again recorded in the table after Example V.

What is claimed is:

1. A method of manufacturing a magnet core suitable for use as a memoryelement in electronic computers comprising the steps of forming amixture of:

74.5-80.0 mol percent Fe -O 12.5-44.6 mol percent Li 0 3.0-8.0 molpercent of Z and up to 6.1 mol percent NiO,

preparing and compacting said mixture into annular bodies, raising thetemperature to said bodies in a heating zone to between 1100 C. nd 1200C. within one minute, maintaining said bodies in said heating zone atsaid temperature for approximately 1 /2 to 8 minutes, and thereaftergradually withdrawing said bodies from said heating zone at asubstantially constant speed to cool said bodies to room temperature inabout 5 to 30 minutes.

2. A method as claimed in claim 1 wherein the bodies are heated to saidtemperature in 30 seconds.

3. A method as claimed in claim 1 wherein said bodies are cooled to roomtemperature in 8 to 20 minutes.

(References on following page) 5 References Cited UNITED STATES PATENTSVan Driel at 211. 252-62.61

Vinal et a1 252-62.61

Esveldt et a1 25262.61

Kitagawa et a1 25262.61

Schmid 25262.61

6 FOREIGN PATENTS 7/1963 Belgium 252-6261 12/1965 Great Britain252-6'2.61 1/1963 U.S.S.R. 25262.61

U.S. C1. X.R.

